const assert = require("assert");

// const hierarchy = ranks => {
//   let result = 0;
//   for (let i = 0; i < ranks.length; i++) {
//     if (ranks.find(v => v === ranks[i] + 1)) {
//       result++;
//     }
//   }
//   return result;
// };

const hierarchy = ranks =>
  ranks.reduce(
    (result, rank, iRank, ranks) =>
      ranks.find(rank => rank === ranks[iRank] + 1) ? result + 1 : result,
    0
  );

// Count how many soldiers have to report to an officer (+1 rank in hierarchy)
// Many soldiers may report to one officer ; cannot report if there is only officers that are more than 1 rank above
assert.strictEqual(hierarchy([2, 2, 3, 0]), 2);
assert.strictEqual(hierarchy([1, 2, 3]), 2);
assert.strictEqual(hierarchy([0, 4, 2]), 0);
assert.strictEqual(hierarchy([3, 4, 3, 0, 2, 2, 3, 0, 0]), 5);
assert.strictEqual(hierarchy([4, 4, 3, 3, 1, 0]), 3);